When installing drywall, one generally must cover a joint between adjacent sheets of drywall with joint tape, then apply a joint compound, commonly referred to as “mud,” over the tape to provide a smoother wall surface. Although the mud can be applied with a drywall knife, this is rather time consuming, so contractors use specialized tools to apply mud at a controlled thickness. The proper drywall tool for a task will depend in part on the angle of the joint between adjacent sheets. If the joint between two adjacent sheets is along a flat wall, a flat finisher is commonly employed. If the joint is in a corner, e.g., a 90° joint between adjacent walls or between the wall and the ceiling, a corner finisher may be employed. Flat finishers and corner finishers are available from a variety of sources, including NorthStar Tool of Burnaby, BC, Canada.
Corner finishers can be used for different purposes at different stages of the drywall installation process. When the joint tape has been applied, the corner finisher may be used to wipe down any excess mud. After this tape sets, the corner finisher may be used to deliver additional mud and provide a uniform, flat finish coat. Corner finishers are typically mounted on a handle using a ball joint so the user can apply consistent pressure as the angle of the handle with respect to the corner finisher changes along the length of the joint.
Some manufacturers provide a series of handles, each having a different length, to allow users to reach different areas of a wall or ceiling. This necessitates detaching one handle and attaching a different handle each time the user needs to reach a different area. When a corner finisher is used to apply the finish coat, the handle typically includes a corner box that includes a supply of mud. When the corner box needs to be refilled, users may prefer to detach the corner finisher from the corner box, which again requires detaching and reattaching the corner finisher to the handle.
Detaching and reattaching the handle from conventional drywall finishers requires that the ball joint be disassembled and reassembled, respectively. There currently are two common techniques for holding the ball joint together. In one approach, a sliding plate is positioned in a groove behind the ball of the ball joint. This plate has a keyway-shaped structure with a narrower width at one end and a wide enough width to allow the ball to pass at its other end. As the finisher gets caked with mud, it can get increasingly difficult to manually slide this plate, which is commonly accomplished by pushing a small tab with a thumb against the force of the cured and partially cured mud between much of the length of the plate and the groove in which the plate is received. The narrow width of the slot, necessary to retain the ball in place, restricts the range of angular movement of the handle with respect to the rest of the tool. From time to time, the shaft of the handle catches the edge of the slot where it changes from the large width for removing the ball to the narrow width for retaining the ball. This can slide the plate forward, risking aligning the ball with the wider part of the plate and dropping the tool.
Some manufacturers take another approach to keep the ball joint together. These manufacturers position a spring-like retaining clip behind the ball and is held in place with a spinner. Manipulating the relatively small spinner and retaining clip can be awkward even when the finisher is clean; the task becomes even more unwieldy as the spinner and clip get caked with mud. The retaining clip will tend to fatigue over time. Eventually, this fatigue will make the retaining clip less secure and significantly increase the risk of dropping the tool off the end of the handle. These relatively costly tools require tight tolerances to ensure a quality finish and dropping the tool can significantly damage the tool, sometimes rendering it unusable.